Abstract
Rapid arrhythmia originating within pulmonary veins (PVs) precipitates atrial fibrillation (AF) in man. To determine a possible basis for an increased incidence of AF observed peri-myocardial infarction in man, we compared AF induction in vivo and triggered arrhythmia formation within isolated PVs in vitro in normal dogs and dogs studied 24 hours postcoronary artery ligation. The incidence of AF initiated by atrial premature stimuli was increased in dogs postcoronary artery ligation (6/9) versus normal (2/12) (P = 0.03). In isolated PVs from normal hearts, pause-dependent early afterdepolarizations (EADs) were enhanced by catecholamines. Rapid arrhythmia (1,182 +/- 213 beats/min) was triggered during isoproterenol/norepinephrine (32 nM) + acetylcholine (100 nM) (N = 16/23) using the same pacing pauses eliciting EADs. Rapid arrhythmia (802 +/- 161 beats/min) was also triggered by local autonomic nerve stimulation (ANS; N = 18/23). Despite equivalent pause-dependent afterdepolarization formation in PVs from infarcted hearts, a rightward 45-fold and 28-fold shift in the dose-response curve for afterdepolarization enhancement was observed for isoproterenol and norepinephrine, respectively (P < 0.02). ANS (N = 1/19) and isoproterenol/norepinephrine (32 nM) + acetylcholine (100 nM) (N = 0/9 and 0/12, respectively) (P = 0.0001) failed to elicit arrhythmia formation. Beta-adrenergic receptor desensitization was associated with a 2.5-fold increase in PV beta-adrenergic receptor kinase (ARK). The data demonstrate decreased susceptibility of isolated canine PVs for arrhythmia triggered by local ANS, or pacing pauses in the presence of a catecholamine + acetylcholine, postmyocardial infarction, despite a greater susceptibility of the intact heart to AF. The decreased arrhythmia susceptibility was observed coincident with an increase in beta-ARK and a decreased responsiveness to beta-adrenergic receptor agonists.
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